This application is for continued funding of a comprehensive project. This study will analyze existing data from 7 major longitudinal growth studies in the United States and Australia in which more than 2,400 individuals were enrolled. Existing cross- sectional data from several U.S. sources will be used to validate prediction equations that will be developed in the project. Important, new serial data will be collected from almost 800 juvenile and adult participants in the Fels Longitudinal Study to extend the serial records and collect additional variables. The major aims of the project are to study changes in body composition with age, the natural history and tracking of body fatness and of fat patterns, to determine and explain the association between fatness and risk factors for disease and levels of physical activity, to evaluate the validity of bioelectric impedance, and the influence of genetic factors on fat-related traits. This will require some methodological studies to improve the way in which body composition is measured. The relations between bioelectric impedance measurements, fat-free mass and total body water will be analyzed and equations developed that predict body composition from data that are easy to obtain and will, therefore, be useful in epidemiologic studies. The long-term goal is to increase understanding of body composition in human beings and its association with risk factors for disease. This work is highly significant and should provide information relevant to the proper timing of preventive measures. Currently, the management of obesity is often inefficient, if judged over long intervals, particularly when a single treatment mode is applied to a heterogenous group of conditions. The proposed research will assist the categorization of obesity on the basis of anthropometry, body composition and persistence. Pubescent changes in body composition and the relationships between risk factors during pubescence and in adulthood will be examined. Some planned analyses pertain to changes with age in the associations between body fatness and frame size particularly in children. Other analyses concern associations between risk factors, e.g., plasma lipids, and variations in the degree and types of body fatness and attempts to identify genetic determinants of traits related to body fatness.